High pressure discharge lamps typically include elongate electrodes extending into a discharge space formed by a glass enclosure. The discharge space includes a rare gas and the electrodes form respectively a cathode and an anode spaced from one another within the discharge space, as is well understood in the art. The electrodes lead outwardly from the glass enclosure and must be sealed hermetically thereto. Since the cathode and anode are held at the free end portions of the elongate electrodes, the weight of the electrodes may tend to damage the hermetic seal to the glass enclosure. Accordingly, elements are often provided to support the electrodes, particularly in lamps operated by direct current.
In the U.S. Pat. No. 3,140,417, the elongate electrodes are made to pass through a sleeve of quartz glass. The glass enclosure of the lamp includes a neck portion which is heated to its softening temperature in the region adjacent the support sleeve and collapsed around the support sleeve to seal the support sleeve and the neck portion together. The support sleeve must be located accurately relative to the neck portion of the glass enclosure, and this tends to complicate assembly. Also, the heating of the neck portion to its softening temperature normally must be done with precision by highly qualified personnel, due to the specific properites of the materials involved. Supporting the electrodes in the manner disclosed in the patent noted above is, therefore, rather complicated and troublesome.
Support elements which are not fused with the glass envelope of the lamp have been proposed, for example as disclosed in U.S. Pat. No. 4,038,578, Mathijssen. In this patent, the support elements may be held in their proper position by deforming a portion of the glass envelope around the support element, or by locking the support element between locking members held to the electrode. Such arrangements, however, are rather cumbersome and also tend to complicate assembly.
Some of these drawbacks of the support elements proposed in the latter patent can be overcome by use of support elements of the type disclosed in U.S. Ser. No. 228,408, now U.S. Pat. No. 4,463,281, which corresponds to German Patent Disclosure Document DE-OS No. 30 29 824, which has a rounded edge pressed by a pressure spring against a constricted portion located between the glass envelope for the electrode and the discharge space. Again, however, such support elements are rather cumbersome to assemble in position.